The present invention relates to a pressure filter adapter and containment vessel for vacuum filter units and the like.
Vacuum filter units are well known in the art and are especially useful in laboratory and analytical work. A typical vacuum filter is shown in U.S. Pat. No. 3,295,686. Briefly, such a unit includes an upper reservoir for the liquid to be filtered, a lower receptacle for receiving the filtrate and an intermediate filter means. These three components are joined to form an integral unit having a fluid tight seal between the outer margins of the filter means, reservoir and receptacle. In addition, the receptacle has a spout for attachment to a vacuum pump or the like. With this arrangement, the receptacle can be partly evacuated in order to facilitate the filtering process. When the evacuation means is disconnected, the spout serves the dual function of allowing the filtrate to be poured from the receptacle.
For some applications, pressure filtration is desired as opposed to vacuum filtration. For example, viscous liquids or liquids with a high particle load which may be difficult to filter using vacuum techniques are often filtered under pressure. Pressure filtration is also used to filter liquids containing dissolved gases such as carbon dioxide. Pressure filtration also eliminates foaming problems often encoutered with vacuum filtration.
To adapt the vacuum filter unit for use as a pressure filter, a cap is provided for the reservoir of the filter unit, the cap having a pressure line connector. In this way the volume of the reservoir over the liquid can be pressurized to force the liquid down through the filter means and into the receptacle.
Whenever a vacuum filter unit is used for pressure filtration, there are several safety procedures which should be observed. For example, the filter unit should be contained behind an appropriate shield. This protects against explosion and personal or property injury resulting from particles of the filter unit or from the liquids being filtered in the event such liquid contain corrosive materials or biological agents. Since the fluid being filtered under pressure is often viscous and relatively dense, it tends to make the filter unit top heavy when the liquid to be filtered is placed into the reservoir. For this reason, it is preferred that the filter unit be restrained or fixed in position so as to prevent tipping and spilling of the contents.
Each vacuum filter unit usually comes pre-sterilized and with a cotton plug inserted into the receptacle spout. This cotton plug prevents air borne bacteria or other organisms from entering into the receptacle and contaminating the filtrate. The plug is maintained in the spout during vacuum filtration and is removed only under sterile conditions prior to pouring the filtrate from the receptacle. During pressure filtration, it is possible for the pressure within the receptacle to push the plug out of the spout. Accordingly, care must be taken to insure that the cotton plug remains in position during pressure filtration.
The present invention allows the vacuum filter unit to be used as a pressure filter with relative safety and convenience by providing complete containment and support for the filter unit throughout the pressure filtration process.